EPA Vastly Misjudges Methane Leaks, Study Confirms

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The federal government has underestimated methane emissions from
the United States by 50 percent for the past 20 years, according
to a comprehensive new study.

Methane, also called natural gas, is a powerful but short-lived
greenhouse
gas. It lasts just nine years in Earth's atmosphere but is
about 34 times more potent at trapping infrared radiation (the
greenhouse effect) than carbon dioxide, which is more abundant
and lasts longer. While methane spews into the sky from both
natural sources, such as wetlands, and human activities,
including oil and gas production, the government estimates only
track manmade sources.

The review of scientific studies of
methane emissions suggests that Environmental Protection
Agency (EPA) methane counts are about 50 percent too low, though
the underestimate could range from 25 percent to as much as 75
percent. That means the United States is pumping about 14 million
tons more methane than thought into the atmosphere each year,
according to the findings, published today (Feb. 13) in the
journal Science.

"Evidence from numerous studies consistently suggest that methane
emissions are larger than those estimated by the EPA inventory,"
said Adam Brandt, lead study author and an energy resources
engineer at Stanford University in Palo Alto, Calif.

The review analyzed the results of more than 200 studies that
traced
methane emissions across the United States and were published
in the past 20 years. The results were compared to the EPA's
Greenhouse Gas Inventory, which records methane emissions and
other climate-changing gases.

This isn't the first time a serious discrepancy has shown up
between official methane estimates and a scientific study. For
example, the EPA's "bottom-up" approach, which measures natural
gas outputs directly from the source, can come up with vastly
different figures than "top-down" studies, which measure
air-borne gas concentrations. A study published in the journal
Proceedings of the National Academy of Sciences in November 2013
using the top-down approach also
found a 50 percent underestimate.

"There have been a lot of studies that … superficially, have
seemingly contradictory results," Brandt said. "Really, they were
performed at different scales with different methodologies."

The new study sought to synthesize the results of both
approaches, and provide a better estimate of natural gas
emissions across the United States. It was funded by Novim, a
nonprofit group aimed at providing scientific data on major world
problems, through a grant from the Cynthia and George Mitchell
Foundation.

Natural gas as fuel

One of the biggest U.S. methane emitters is the natural gas
industry. Leaks come from drilling for oil and gas, refining
plants and transport and distribution, such as pipelines.

The study finds that just a small number of super-emitters in the
natural gas industry are likely responsible for more than half of
the industry's methane leaks. Finding these super-emitters, which
account for less than 1 percent of all leaking devices, is a
challenge for industry, Brandt said. "There's about a half a
million wells and a couple million miles of pipeline, so it's a
very big and very complex system," he said. "But if they know
where the leak is they want to fix it, because it's costing them
money." Greenhouse
Gases: The Biggest Emitters (Infographic)

Cleaning up leaks would finally make natural gas cleaner than
diesel, the study finds. Currently, the leaks in the gas system
mean that running trucks and buses on diesel is still cleaner
than natural gas, the researchers said.

But even though the natural gas system is sloppier than the EPA
estimates, it's still cleaner than coal, the study concludes.
Switching to coal-fired power plants over natural gas would
produce more climate warming, even if the natural gas system was
responsible for all of the
U.S. methane leaks reported in the study, the researchers
said.

In response to concerns about natural gas extraction leakage, the
EPA is considering tightening federal regulations on oil and gas
drilling to reduce methane emissions.

An agency spokesperson said the study results have not been
reviewed yet. "EPA is aware of methane studies that result in
estimates of national methane emissions that differ from EPA's
estimates, and is interested in feedback on how information from
such studies can be used to improve U.S. GHG [greenhouse gas]
Inventory estimates," the agency said in a statement.